Perforation of a difficult-to-cut material, for which is mechanical machining is difficult, is generally performed by an electrochemical machining method or an electro-discharge processing method. In particular, when the difficult-to-cut material having a high aspect ratio is perforated, the electrochemical machining method is used.
Here, for example, in a turbine blade of a gas turbine, a cooling hole configured to flow a coolant to cool the turbine blade is formed. In order to increase cooling efficiency by the cooling hole, a shape of the cooling hole may be curved along a geometrical shape of the turbine blade. However, while the electrochemical machining method with respect to the turbine blade of the related art is appropriate for formation of a linear hole, it is difficult to form a machined hole having a curved shape, i.e., a curved hole. Here, when the cooling hole is formed in the turbine blade, two linear holes are respectively formed to be connected to form a pseudo-curved hole.
Meanwhile, for example, in Patent Literature 1, a curved hole machining apparatus configured to machine a curved hole is disclosed. In the curved hole machining apparatus, a difference in a machining amount is generated at a position in a circumferential direction of a machining electrode tool by covering a surface of the machining electrode tool by an insulating member except for a portion thereof. Accordingly, as the machining electrode tool moves toward a side at which a machining amount is large, the curved hole is formed.